Methods for depositing films on sensitive substrates

ABSTRACT

Methods and apparatus to form films on sensitive substrates while preventing damage to the sensitive substrate are provided herein. In certain embodiments, methods involve forming a bilayer film on a sensitive substrate that both protects the underlying substrate from damage and possesses desired electrical properties. Also provided are methods and apparatus for evaluating and optimizing the films, including methods to evaluate the amount of substrate damage resulting from a particular deposition process and methods to determine the minimum thickness of a protective layer. The methods and apparatus described herein may be used to deposit films on a variety of sensitive materials such as silicon, cobalt, germanium-antimony-tellerium, silicon-germanium, silicon nitride, silicon carbide, tungsten, titanium, tantalum, chromium, nickel, palladium, ruthenium, or silicon oxide.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority to U.S. patentapplication Ser. No. 15/650,662 filed Jul. 14, 2017, titled “METHODS FORDEPOSITING FILMS ON SENSITIVE SUBSTRATES,” which is a divisional of U.S.application Ser. No. 15/015,952 (issued as U.S. Pat. No. 9,786,570),filed Feb. 4, 2016, titled “METHODS FOR DEPOSITING FILMS ON SENSITIVESUBSTRATES,” which is a divisional of U.S. patent application Ser. No.14/074,617 (issued as U.S. Pat. No. 9,287,113), filed Nov. 7, 2013,titled “METHODS FOR DEPOSITING FILMS ON SENSITIVE SUBSTRATES,” whichclaims benefit of priority to U.S. Provisional Patent Application No.61/724,217, filed Nov. 8, 2012, and titled “METHODS FOR DEPOSITING FILMSON SENSITIVE SUBSTRATES,” each of which is incorporated herein byreference in its entirety and for all purposes.

BACKGROUND

One of the processes frequently employed during the fabrication ofsemiconductor devices is the deposition of various films such as oxidesand nitrides onto a substrate. In some cases, the substrate isparticularly sensitive to oxidation or nitridation during thedeposition, which can damage the substrate. This sensitivity isespecially likely to arise in applications such as gapfill anddouble-patterning, though it may be problematic in other contexts aswell. Examples of sensitive substrates include silicon (Si), cobalt(Co), germanium-antimony-tellerium alloy (GST), silicon-germanium(SiGe), silicon nitride (SiN), silicon carbide (SiC), and silicon oxide(SiO₂). As such, there exists a need for a method of depositingsemiconductor films that prevents damage to sensitive substrates. Insome embodiments, the method prevents oxidation of oxidation-sensitivesubstrates, and/or nitridation of nitridation-sensitive substrates.

SUMMARY

Various aspects disclosed herein pertain to methods of depositing a filmon an exposed surface of an oxidation-sensitive substrate surface. Thesemethods typically include surface mediated reactions in which a film isgrown over multiple cycles of reactant adsorption and reaction. In onesuch aspect, the method is characterized by the following operations:(a) exposing the oxidation-sensitive substrate to a silicon-containingreactant in vapor phase; (b) exposing the oxidation-sensitive substrateto an oxidizing reactant in vapor phase in a station of a reactionchamber; and (c) periodically igniting a plasma in the reaction chamberusing a high frequency radio frequency between about 12.5 and 125W/station when the flow of the silicon-containing reactant has ceased.In some implementations of this method, the oxidizing reactant flowscontinuously to the substrate and the silicon-containing reactant flowsintermittently to the substrate. In other implementations, the oxidizingreactant is pulsed into the reaction chamber.

In some implementations, the thickness of the resulting silicon oxidefilm is between about 10-50 Å. In some embodiments, the substrate iskept between about 25-450° C., and in some cases is kept between about25-100° C., between about 50-150° C., or between about 50-200° C. Theoxidation reactant may be a mixture of oxygen (O₂) and a weak oxidizersuch as nitrous oxide (N₂O), carbon monoxide (CO), carbon dioxide (CO₂),nitric oxide (NO), nitrogen dioxide (NO₂), sulfur oxide (SO), sulfurdioxide (SO₂), oxygen-containing hydrocarbons (C_(x)H_(y)O_(z)) and/orwater (H₂O). In other implementations, the oxidation reactant may beentirely weak oxidizer. Alternatively, the oxidation reactant mayinclude ozone (O₃). In some embodiments, the oxidation reactant is about0-50% O₂ and about 50-100% weak oxidizer. The radio frequency may befurther limited in some implementations to between 50 and 125 W/station.

In some embodiments, the method described above is further characterizedby the deposition of a second silicon oxide material through thefollowing sequence of operations: (d) exposing the oxidation-sensitivesubstrate to a second silicon-containing reactant in vapor phase; (e)exposing the oxidation-sensitive substrate to a second oxidizingreactant in vapor phase; and (f) periodically igniting the plasma in thereaction chamber using a high frequency radio frequency between about250 and 1500 W/station when the vapor phase flow of the secondsilicon-containing reactant has ceased. In some implementations,operations (d)-(f) are performed between about 50 and 400° C., while insome cases these operations are limited to 150-250° C. or 300-400° C.While operations (a)-(f) may be performed isothermally in someembodiments, in other embodiments operations (a)-(c) and operations(d)-(f) are performed at different temperatures.

In some implementations, the first silicon oxide material and the secondsilicon oxide material each form layers of a bilayer. The first siliconoxide material may be referred to as the protective layer, and thesecond silicon oxide material may be referred to as the electricallyfavorable layer. In one embodiment, the thickness of the protectivelayer is between about 1 and about 20% of the total thickness of thebilayer.

In one embodiment, operations (a)-(c) and operations (d)-(f) utilize thesame rate and/or composition of vapor phase flow of thesilicon-containing reactant. In other embodiments, either the rateand/or the composition of the vapor phase flow of the silicon-containingreactant will be different between the two sets of operations.Specifically, in one implementation, the vapor phase flow ofsilicon-containing reactant during operations (d)-(f) contains a higherpercentage of O₂ as compared to the flow during operations (a)-(c).Though in some embodiments the vapor phase flow of oxidizing reactant iscontinuous, in other embodiments this flow is pulsed into the reactionchamber.

While many of the specifically disclosed operations relate to asilicon-based oxidation-sensitive substrate, the methods may be used onmany different types of oxidation sensitive substrate surfaces. Group4-11 metals, silicon, amorphous silicon, carbon films (including filmsdeposited through plasma enhanced chemical vapor deposition or spin ontechniques, for example), and group III-V materials are likely to besensitive substrates. For example, in some implementations the substratesurface may be Cobalt (Co), germanium-antimony-tellerium,silicon-germanium, silicon nitride, silicon carbide, tungsten (W),titanium (Ti), tantalum (Ta), chromium (Cr), nickel (Ni), palladium(Pd), ruthenium (Ru), or silicon oxide. One of ordinary skill in the artwould understand that the methods described herein can be used on avariety of oxidation-sensitive substrates not limited to those mentionedabove.

In some implementations, no more than about 2 Å of theoxidation-sensitive substrate is oxidized.

In another aspect, a method of forming a silicon oxide material on anexposed surface of an oxidation-sensitive substrate may be characterizedby the following sequence of operations: (a) exposing theoxidation-sensitive substrate to a silicon-containing reactant in vaporphase; (b) exposing the oxidation-sensitive substrate to an oxidationreactant in vapor phase in a station of a reaction chamber maintainedbetween about 25-200° C.; and (c) igniting a plasma in the reactionchamber when the vapor phase flow of the silicon-containing reactant hasceased.

In one embodiment, the resulting silicon oxide material is between about10 and about 50 Å. According to various implementations, the plasma isignited using a high frequency radio frequency between about 12.5 andabout 125 W/station and in some implementations this range is limited tobetween about 50 and about 125 W/station.

The oxidation reactant may be a mixture of O₂ and weak oxidizer such asN₂O, CO, CO₂, NO, NO₂, SO, SO₂, C_(x)H_(y)O_(z) and/or H₂O. In otherimplementations, the oxidation reactant may be entirely weak oxidizer.Alternatively, the oxidation reactant may include O₃. In someembodiments, the oxidation reactant is about 0-50% O₂ and about 50-100%weak oxidizer.

In some embodiments, the method described above is further characterizedby the deposition of a second silicon oxide material through thefollowing sequence of operations: (d) exposing the oxidation-sensitivesubstrate to a second silicon-containing reactant in vapor phase in astation of a reaction chamber maintained at a temperature at least about50° C. higher than during operations (a)-(c); (e) exposing theoxidation-sensitive substrate to a second vapor phase flow of a secondoxidation reactant; and (f) igniting the plasma in the reaction chamberusing a high frequency radio frequency when the vapor phase flow of thesecond silicon-containing reactant has ceased.

In some implementations, steps (d)-(f) are performed between about 300and about 400° C. In some embodiments, the first silicon oxide materialand the second silicon oxide material each form layers of a bilayer. Thefirst silicon oxide material may be referred to as the protective layer,and the second silicon oxide material may be referred to as theelectrically favorable layer. In one embodiment, the thickness of theprotective layer is between about 1 and about 20% of the total thicknessof the bilayer.

While many of the specifically disclosed operations relate to asilicon-based oxidation-sensitive substrate, the methods may be used onmany different types of oxidation sensitive substrate surfaces. Forexample, in some implementations the substrate surface may be cobalt,germanium-antimony-tellerium, silicon-germanium, silicon nitride,silicon carbide, or silicon oxide. One of ordinary skill in the artwould understand that the methods described herein can be used on avariety of oxidation-sensitive substrates not limited to those mentionedabove.

In one implementation, no more than 2 Å of the oxidation-sensitivesubstrate is oxidized. In some embodiments, operation (f) is performedat RF power between about 250-1500 W/station.

In another aspect, a method of forming a silicon-containing bilayer on areaction-sensitive substrate may be characterized by the followingoperations: (a) forming a first layer of a silicon-containing filmthrough a plasma-enhanced atomic layer deposition process; and (b)forming a second layer of the silicon-containing film on the first layerby a plasma-enhanced atomic layer deposition process performed using ahigher radio frequency power than that used in operation (a). In adifferent aspect, a method of forming a silicon-containing bilayer on areaction-sensitive substrate may be characterized by the followingoperations: (a) forming a first layer of a silicon-containing filmthrough a plasma-enhanced atomic layer deposition process; and (b)forming a second layer of the silicon-containing film on the first layerby a plasma-enhanced atomic layer deposition process performed using ahigher temperature than that used during operation (a). As noted above,the first layer may be referred to as the protective layer and thesecond layer may be referred to as the electrically favorable layer.

In one embodiment of these methods, the thickness of the protectivelayer is between about 1 and about 20% of the total thickness of thebilayer. In one implementation, the thickness of the protective layer isbetween about 10 and about 50 Å.

The oxidation reactant may be a mixture of O₂ and weak oxidizer such asN₂O, CO, CO₂, NO, NO₂, SO, SO₂, C_(x)H_(y)O_(z) and/or H₂O. In otherimplementations, the oxidation reactant may be entirely weak oxidizer.Alternatively, the oxidation reactant may include O₃. In someembodiments, the oxidation reactant is about 0-50% O₂ and about 50-100%weak oxidizer.

While many of the specifically disclosed operations relate to asilicon-based oxidation-sensitive substrate, the methods may be used onmany different types of oxidation sensitive substrate surfaces. Forexample, in some implementations the substrate surface may be cobalt,germanium-antimony-tellerium, silicon-germanium, silicon nitride,silicon carbide, or silicon oxide. One of ordinary skill in the artwould understand that the methods described herein can be used on avariety of oxidation-sensitive substrates not limited to those mentionedabove. In some embodiments, the silicon-containing film is a siliconoxide, a silicon nitride, a silicon carbide, a silicon oxynitride, or asilicon carbide film.

These and other features will be described below with reference to theassociated drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1E provide example timing diagrams for depositing filmsaccording to certain disclosed embodiments.

FIG. 2 shows experimental data illustrating oxidation damage to asubstrate.

FIG. 3A shows film thickness vs. the number of deposition cycles forfilms deposited at different levels of radio frequency (RF) flux.

FIG. 3B shows the amount of substrate oxidation at different levels ofRF flux and different ratios of O₂:weak oxidizer delivered duringdeposition.

FIG. 4 shows data related to breakdown voltage vs. relative thickness ofa protective layer.

FIG. 5 shows data related to film densification, which may be used todetermine the minimum thickness of a protective layer.

FIG. 6 illustrates a reaction chamber for performing atomic layerdeposition according to certain disclosed embodiments.

FIG. 7 illustrates a multi-tool apparatus that may be used to depositfilms according to certain disclosed embodiments.

DETAILED DESCRIPTION

In this application, the terms “semiconductor wafer,” “wafer,”“substrate,” “wafer substrate,” and “partially fabricated integratedcircuit” are used interchangeably. One of ordinary skill in the artwould understand that the term “partially fabricated integrated circuit”can refer to a silicon wafer during any of many stages of integratedcircuit fabrication thereon. A wafer or substrate used in thesemiconductor device industry typically has a diameter of 200 mm, or 300mm, or 450 mm. The following detailed description assumes the inventionis implemented on a wafer. However, the invention is not so limited. Thework piece may be of various shapes, sizes, and materials. In additionto semiconductor wafers, other work pieces that may take advantage ofthis invention include various articles such as printed circuit boardsand the like.

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the presented embodiments.The disclosed embodiments may be practiced without some or all of thesespecific details. In other instances, well-known process operations havenot been described in detail to not unnecessarily obscure the disclosedembodiments. While the disclosed embodiments will be described inconjunction with the specific embodiments, it will be understood that itis not intended to limit the disclosed embodiments.

Various aspects disclosed herein pertain to methods of depositing a filmon a substrate surface. These methods include plasma-activatedsurface-mediated reactions in which a film is grown over multiple cyclesof reactant adsorption and reaction. In some implementations, themethods are conformal film deposition (CFD) reactions, with a CFDreaction in which one more reactants adsorb to the substrate surface andthen react to form a film on the surface by interaction with plasma.

Conventional methods of depositing oxide layers can result in oxidationdamage to sensitive substrates. This damage is problematic for certainapplications including, but not limited to, gapfill anddouble-patterning.

Provided herein are CFD processes and other deposition processes thatprevent the oxidation of the substrate on which they are deposited. Alsoprovided are CFD processes and other deposition processes that preventnitridation of, or other reaction with, an underlying substrate.Generally speaking, the processes may be used to reduce or eliminateunwanted reactions with the sensitive substrate and conversion of aportion of the sensitive substrate to another material. These processesmay be especially useful for sensitive substrates such as silicon (Si),cobalt (Co), germanium-antimony-tellerium alloy (GST), silicon-germanium(SiGe), silicon nitride (SiN), silicon carbide (SiC), and silicon oxide(SiO₂), and film types such as SiO₂, SiN, SiCN, SiC, noble metals, andhigh K materials including lanthanide-oxides, group 4 metal oxides, andgroup 5 metal oxides.

In certain embodiments, the damage to the substrate is prevented throughthe deposition of a thin protective layer, which may be deposited at arelatively low temperature, and/or at a relatively low pressure, and/orat a relatively low level of RF power/flux. In some cases, theprotective layer is incorporated into a bilayer structure where thebottom layer is the protective layer and the top layer is anelectrically favorable layer. As compared to the electrically favorablelayer, the protective layer may be deposited at a lower temperature,and/or lower RF power, and/or shorter RF time, and/or lower pressure,and/or with a different reactant. These deposition conditions may helpprevent damage to the underlying substrate while producing an operabledevice.

Furthermore, various embodiments provided herein relate to methods forevaluating substrate oxidation using a common silicon substrate as atest vehicle, thereby avoiding the complexity of testing oxidation ondevice substrates.

Also, various embodiments provided herein relate to methods fordetermining the minimal thickness of a bottom protective layer in abilayer approach, which thickness will provide adequate protectionagainst substrate oxidation while having minimal impact on bulk filmelectrical properties.

U.S. patent application Ser. No. 13/084,399, filed Apr. 20, 2011, andtitled “PLASMA ACTIVATED CONFORMAL FILM DEPOSITION,” which is hereinincorporated by reference in its entirety, describes CFD reactionsincluding timing diagrams for various embodiments of plasma-activatedCFD processes in which a substrate is exposed to reactants A and B. Themethods described herein include such CFD processes. While thedescription below refers chiefly to the deposition of silicon oxidefilms from a silicon-containing reactant such asbis(tert-butylamino)silane (BTBAS) and an oxidant reactant, also knownas an oxidation reactant, such as oxygen, nitrous oxide or a mixturethereof, the methods described herein may also be used forplasma-activated deposition of other types of films including but notlimited to silicon nitrides. Reactants and process flows for thedeposition of silicon nitrides and other film types are described in theSer. No. 13/084,399 application, as well as in U.S. patent applicationSer. No. 13/084,305, filed Apr. 11, 2011, and titled “SILICON NITRIDEFILMS AND METHODS,” which is herein incorporated by reference in itsentirety.

Manufacture of semiconductor devices typically involves depositing oneor more thin films on a non-planar substrate in an integratedfabrication process. In some aspects of the integrated process it may beuseful to deposit thin films that conform to substrate topography. Forexample, a silicon nitride film may be deposited on top of an elevatedgate stack to act as a spacer layer for protecting lightly-doped sourceand drain regions from subsequent ion implantation processes.

In spacer layer deposition processes, chemical vapor deposition (CVD)processes may be used to form a silicon nitride film on the non-planarsubstrate, which is then anisotropically etched to form the spacerstructure. However, as a distance between gate stacks decreases, masstransport limitations of CVD gas phase reactions may cause“bread-loafing” deposition effects. Such effects typically exhibitthicker deposition at top surfaces of gate stacks and thinner depositionat the bottom corners of gate stacks. Further, because some die may haveregions of differing device density, mass transport effects across thewafer surface may result in within-die and within-wafer film thicknessvariation. These thickness variations may result in over-etching of someregions and under-etching of other regions. This may degrade deviceperformance and/or die yield.

Some approaches to addressing these issues involve atomic layerdeposition (ALD). In contrast with a CVD process, where thermallyactivated gas phase reactions are used to deposit films, ALD processesuse surface-mediated deposition reactions to deposit films on alayer-by-layer basis. In one example ALD process, a substrate surface,including a population of surface active sites, is exposed to a gasphase distribution of a first film precursor (P1). Some molecules of P1may form a condensed phase atop the substrate surface, includingchemisorbed species and physisorbed molecules of P1. The reactor is thenevacuated to remove gas phase and physisorbed P1 so that onlychemisorbed species remain. A second film precursor (P2) is thenintroduced to the reactor so that some molecules of P2 adsorb to thesubstrate surface. The reactor may again be evacuated, this time toremove unbound P2. Subsequently, thermal energy provided to thesubstrate activates surface reactions between adsorbed molecules of P1and P2, forming a film layer. Finally, the reactor is evacuated toremove reaction by-products and possibly unreacted P1 and P2, ending theALD cycle. Additional ALD cycles may be included to build filmthickness.

Depending on the exposure time of the precursor dosing steps and thesticking coefficients of the precursors, each ALD cycle may deposit afilm layer of, in one example, between one-half and three angstromsthick.

Conformal films may also be deposited on planar substrates. For example,antireflective layers for lithographic patterning applications may beformed from planar stacks comprising alternating film types. Suchantireflective layers may be approximately 100 to 1000 angstroms thick,making slower ALD processes less attractive than faster CVD processes.However, such anti-reflective layers may also have a lower tolerance forwithin-wafer thickness variation than many CVD processes may provide.For example, a 600-angstrom thick antireflective layer may tolerate athickness range of less than 3 angstroms.

Various embodiments are provided herein providing processes andequipment for plasma-activated ALD and conformal film deposition (CFD)on non-planar and planar substrates. These embodiments are typicallyperformed at relatively low temperature, and/or at a relatively lowpressure, and/or at a relatively low level of RF power/flux (i.e., lowdamage conditions). In some cases, a bilayer approach is used such thata bottom protective layer is formed at low damage conditions, and anupper electrically favorable layer is formed at different conditions.

As indicated above, embodiments described herein can include CFDprocesses as well as ALD processes. Generally, CFD does not rely oncomplete purges of one or more reactants prior to reaction to form thefilm. For example, there may be one or more reactants present in thevapor phase when a plasma (or other activation energy) is struck.Accordingly, one or more of the process steps described in an ALDprocess may be shortened or eliminated in an example CFD process.Further, in some embodiments, plasma activation of deposition reactionsmay result in lower deposition temperatures than thermally-activatedreactions, potentially reducing the thermal budget of an integratedprocess. While embodiments include CFD, the methods described herein arenot limited to CFD. Other suitable methods include ALD.

For context, a short description of CFD is provided. The concept of aCFD “cycle” is relevant to the discussion of various embodiments herein.Generally a cycle is the minimum set of operations required to perform asurface deposition reaction one time. The result of one cycle isproduction of at least a partial film layer on a substrate surface.Typically, a CFD cycle will include only those steps necessary todeliver and adsorb each reactant to the substrate surface, and thenreact those adsorbed reactants to form the partial layer of film. Ofcourse, the cycle may include certain ancillary steps such as sweepingone or more of the reactants or byproducts and/or treating the partialfilm as deposited. Generally, a cycle contains only one instance of aunique sequence of operations. As an example, a cycle may include thefollowing operations: (i) delivery/adsorption of reactant A, (ii)delivery/adsorption of reactant B, (iii) sweep B out of the reactionchamber, and (iv) apply plasma to drive a surface reaction of A and B toform the partial film layer on the surface.

The description herein uses the terms “principal” and “auxiliary”reactants. As used herein, a principal reactant contains an element thatis solid at room temperature, which element is contributed to the filmformed by CFD. Examples of such elements are metals (e.g., aluminum,titanium, etc.), semiconductors (e.g., silicon and germanium), andnon-metals or metalloids (e.g., boron). As used herein, an auxiliaryreactant is any reactant that is not a principal reactant. The termco-reactant is sometimes used to refer to auxiliary reactants. Examplesof auxiliary reactants include oxygen, ozone, hydrogen, carbon monoxide,nitrous oxide, ammonia, alkyl amines, and the like.

The embodiments herein may use various different process sequences. Onepossible process includes the following sequence of operations: (1) flowauxiliary reactant continuously, (2) provide dose of silicon-containingor other principle reactant, (3) purge 1, (4) expose substrate to RFplasma, (5) purge 2. Another alternative process includes the followingsequence of operations: (1) flow inert gas continuously, (2) providedose of silicon-containing or other principle reactant, (3) purge 1, (4)expose substrate to RF plasma while providing dose of oxidant or otherauxiliary reactant, (5) purge 2. Other example process flows are shownin FIGS. 1A-1E.

The compounds, flow rates, and dosage times provided herein areexamples. Any appropriate silicon-containing reactant and oxidant may beused for the deposition of silicon oxides. Similarly, for the depositionof silicon nitrides, any appropriate silicon-containing reactant andnitrogen-containing reactant may be used. Further, for the deposition ofmetal oxides or metal nitrides, any appropriate metal-containingreactants and co-reactants may be used. The techniques herein arebeneficial in implementing a wide variety of film chemistries. Flowrates and times outside the ranges provided may be appropriate incertain embodiments. Example flow rates are given for 300 mm wafers andmay be scaled appropriately for wafers of other sizes. Other processflows may also be used, some of which are described with reference tothe timing diagrams shown in FIGS. 1A and 1B, below.

In some cases, one of the reactants may be delivered continuously (e.g.,even during delivery of other reactants and/or during plasma exposure).The continuously flowing reactant may be delivered to the reactionchamber in conjunction with a carrier gas—e.g., argon. In some cases,the delivery of the continuously flowing reactants to reaction chamberis controlled by using divert valve/inlet valve toggling. Gas flowchanges may be diverted or co-flowed. In one example, a continuouslyflowing reactant is periodically diverted from the reaction chamber suchthat it is only delivered to the reaction chamber at certain periods.The continuously flowing gas may be diverted to an outlet/dump usingappropriate valves. For instance, an oxidizing reactant may flowcontinuously, but only be delivered to the reaction chamberperiodically. When the oxidizing reactant is not being delivered to thereaction chamber, it may be diverted to an outlet, recycle system, etc.

One advantage of the continuous flow embodiment is that the establishedflow avoids the delays and flow variations caused by transientinitialization and stabilization of flow associated with turning theflow on and off.

As a specific example, an oxide film may be deposited by a conformalfilm deposition process using a principal reactant (sometimes referredto as a “solid component” precursor or, in this example, simply“reactant B”). Bis(tert-butylamino)silane (BTBAS) is one such principalreactant. In this example, the oxide deposition process involvesdelivery of an oxidant such as oxygen or nitrous oxide, which flowsinitially and continuously during delivery of the principal reactant indistinct exposure phases. The oxidant also continues to flow duringdistinct plasma exposure phases. See for example the sequence depictedin FIG. 1A.

In some specific examples, the reactant that flows continuously is anauxiliary reactant. The continuously flowing reactant may be provided ata constant flow rate or at varied but controlled flow rate. In thelatter case, as an example, the flow rate of an auxiliary reactant maydrop during an exposure phase when the primary reactant is delivered.For example, in oxide deposition, the oxidant (e.g., oxygen or nitrousoxide) may flow continuously during the entire deposition sequence, butits flow rate may drop when the primary reactant (e.g., BTBAS) isdelivered. This increases the partial pressure of BTBAS during itsdosing, thereby reducing the exposure time needed to saturate thesubstrate surface. Shortly before igniting the plasma, the flow ofoxidant may be increased to reduce the likelihood that BTBAS is presentduring the plasma exposure phase. In some embodiments, the continuouslyflowing reactant flows at a varied flow rate over the course of two ormore deposition cycles. For example, the reactant may flow at a firstflow rate during a first CFD cycle and at a second flow rate during asecond CFD cycle. In various embodiments, a first set of reaction cyclesis performed under certain deposition conditions to deposit a firstfilm, and a second set of reaction cycles is then performed underdifferent conditions to deposit a second film on the first film. The twofilms may have different properties; for example, the second film havingproperties that are more electrically favorable for the desiredapplication.

Where multiple auxiliary reactants are used, they can be mixed prior todelivery to the reaction chamber, or delivered as separate streams. Insome embodiments, the auxiliary reactant is delivered continuously withan inert gas flow delivered in a burst for purge operations. In someembodiments, an inert gas flow may be continuous, with or without theinert gas flow rate increased for the purge operation. An optional purgecan occur after the plasma is extinguished.

The concept of a CFD “sweep” or “purge” step or phase appears in thediscussion various embodiments herein. Generally, a sweep phase removesor purges one of the vapor phase reactant from a reaction chamber andtypically occurs only after delivery of such reactant is completed. Inother words, that reactant is no longer delivered to the reactionchamber during the sweep phase. However, the reactant remains adsorbedon the substrate surface during the sweep phase. Typically, the sweepserves to remove any residual vapor phase reactant in the chamber afterthe reactant is adsorbed on the substrate surface to the desired level.A sweep phase may also remove weakly adsorbed species (e.g., certainprecursor ligands or reaction by-products) from the substrate surface.In ALD, the sweep phase has been viewed as necessary to prevent gasphase interaction of two reactants or interaction of one reactant with athermal, plasma or other driving force for the surface reaction. Ingeneral, and unless otherwise specified herein, a sweep/purge phase maybe accomplished by (i) evacuating a reaction chamber, and/or (ii)flowing gas not containing the species to be swept out through thereaction chamber. In the case of (ii), such gas may be, for example, aninert gas or an auxiliary reactant such as a continuously flowingauxiliary reactant.

Different embodiments may implement sweep phases at different times. Forexample, in certain cases a sweep step may occur at any of the followingtimes: (1) after delivery of a principal reactant, (2) between pulses ofdelivering a principal reactant, (3) after delivery of an auxiliaryreactant, (4) before plasma exposure, (5) after plasma exposure, and (6)any combination of (1)-(5). Some of these timeframes may overlap. It hasbeen shown that a first sweep performed after delivery of the principalreactant, and a second sweep performed after plasma excitation, areparticularly useful in depositing uniform films.

Unlike many other deposition processes, particularly those requiringthermal activation, the CFD process may be conducted at a relatively lowtemperature. Generally, the CFD temperature will be between about 20 and400 C. Such temperature may be chosen to permit deposition in thecontext of a temperature sensitive process such as deposition on aphotoresist core. In a specific embodiment, a temperature of betweenabout 20 and 100 C is used for double patterning applications (using,e.g., photoresist cores). In another embodiment, a temperature ofbetween about 200 and 350 C is employed for memory fabricationprocessing. In some implementations, a first set of reaction cycles isperformed at a first temperature, and a second set of reaction cycles isperformed at a second temperature that is higher than the firsttemperature.

As suggested above, CFD is well suited for depositing films in advancedtechnology nodes. Thus, for example, CFD processing may be integrated inprocesses at the 32 nm node, the 22 nm node, the 16 nm node, the 11 nmnode, and beyond any of these. These nodes are described in theInternational Technology Roadmap for Semiconductors (ITRS), the industryconsensus on microelectronic technology requirements for many years.Generally they reference one-half pitch of a memory cell. In a specificexample, the CFD processing is applied to “2X” devices (having devicefeatures in the realm of 20-29 nm) and beyond.

While most examples of CFD films presented herein concern silicon basedmicroelectronic devices, the films may also find application in otherareas. Microelectronics or optoelectronics using non-siliconsemiconductors such as GaAs and other III-V semiconductors, as well asII-VI materials such as HgCdTe may profit from using the CFD processesdisclosed herein. Applications for conformal dielectric films in thesolar energy field, such as photovoltaic devices, in the electrochromicsfield, and other fields are possible.

Other example applications for CFD films include, but are not limited toconformal low-k films (e.g., k approximately 3.0 or lower in somenon-limiting examples) for back-end-of-line interconnect isolationapplications, conformal silicon nitride films for etch stop and spacerlayer applications, conformal antireflective layers, and copper adhesionand barrier layers. Many different compositions of low-k dielectrics forBEOL processing can be fabricated using CFD. Examples include siliconoxides, oxygen doped carbides, carbon doped oxides, oxynitrides, and thelike.

FIG. 1A schematically shows a timing diagram 100 for an exampleembodiment of a plasma-activated CFD process. Two full CFD cycles aredepicted. As shown, each includes an exposure to reactant A phase 120,directly followed by an exposure to reactant B phase 140, a sweep ofreactant B phase 160, and finally a plasma activation phase 180. Plasmaenergy provided during plasma activation phases 180A and 180B activatesa reaction between surface adsorbed reactant species A and B. In thedepicted embodiments, no sweep phase is performed after one reactant(reactant A) is delivered. In fact, this reactant flows continuouslyduring the film deposition process. Thus, plasma is ignited whilereactant A is in the gas phase. In the depicted embodiment, reactantgases A and B may co-exist in the gas phase without reacting.Accordingly, one or more of the process steps described in the ALDprocess may be shortened or eliminated in this example CFD process. Forexample, sweep steps after A Exposure Phases 120A and 120B may beeliminated.

FIG. 1A also shows an embodiment of a temporal progression of an exampleCFD process phases for various CFD process parameters. FIG. 1A depictstwo example deposition cycles 110A and 110B, though it will beappreciated that any suitable number of deposition cycles may beincluded in a CFD process to deposit a desired film thickness. ExampleCFD process parameters include, but are not limited to, flow rates forinert and reactant species, plasma power and frequency, substratetemperature, and process station pressure.

A CFD cycle typically contains an exposure phase for each reactant.During this “exposure phase,” a reactant is delivered to a processchamber to cause adsorption of the reactant on the substrate surface.Typically, at the beginning of an exposure phase, the substrate surfacedoes not have any appreciable amount of the reactant adsorbed. In FIG.1A, at reactant A exposure phases 120A and B, reactant A is supplied ata controlled flow rate to a process station to saturate exposed surfacesof a substrate. Reactant A may be any suitable deposition reactant;e.g., a principal reactant or an auxiliary reactant. In one examplewhere CFD produces a silicon dioxide film, reactant A may be oxygen.

In the embodiment shown in FIG. 1A, reactant A flows continuouslythroughout deposition cycles 110A and 110B. Unlike a typical ALDprocess, where film precursor exposures are separated to prevent gasphase reaction, reactants A and B are allowed to mingle in the gas phaseof some embodiments of a CFD process. As indicated above, in someembodiments reactants A and B are chosen so that they can co-existencein the gas phase without appreciably reacting with one another underconditions encountered in the reactor prior to application of plasmaenergy or the activation of the surface reaction. In some cases, thereactants are chosen such that (1) a reaction between them isthermodynamically favorable (i.e., Gibb's free energy <0) and (2) thereaction has a sufficiently high activation energy that there isnegligible reaction at the desired deposition temperature absent plasmaexcitation.

Continuously supplying reactant A to the process station may reduce oreliminate a reactant A flow rate turn-on and stabilization time comparedto an ALD process where reactant A is first turned on, then stabilizedand exposed to the substrate, then turned off, and finally removed froma reactor. While the embodiment shown in FIG. 1A depicts reactant Aexposure phases 120A and B as having a constant flow rate, it will beappreciated that any suitable flow of reactant A, including a variableflow, may be employed within the scope of the present disclosure.Further, while FIG. 1A shows reactant A having a constant flow rateduring the entire CFD cycle (deposition cycle 110A), this need not bethe case. For example, the flow rate of reactant A may decrease during Bexposure phases 140A and 140B. This may increase the partial pressure ofB and thereby increase the driving force of reactant B adsorbing on thesubstrate surface. In other cases, reactants A and B may each bedelivered in doses (i.e., neither reactant flows continuously).

In some embodiments, reactant A exposure phase 120A may have a durationthat exceeds a substrate surface saturation time for reactant A. Forexample, the embodiment of FIG. 1A includes a reactant A post-saturationexposure time 130 in reactant A exposure phase 120A. Optionally,reactant A exposure phase 120A includes a controlled flow rate of aninert gas. Example inert gases include, but are not limited to,nitrogen, argon, and helium. The inert gas may be provided to assistwith pressure and/or temperature control of the process station,evaporation of a liquid precursor, more rapid delivery of the precursorand/or as a sweep gas for removing process gases from the processstation and/or process station plumbing.

At Reactant B exposure phase 140A of the embodiment shown in FIG. 1A,reactant B is supplied at a controlled flow rate to the process stationto saturate the exposed substrate surface. In one example silicondioxide film, reactant B may be BTBAS. While the embodiment of FIG. 1Adepicts reactant B exposure phase 140A as having a constant flow rate,it will be appreciated that any suitable flow of reactant B, including avariable flow, may be employed within the scope of the presentdisclosure. Further, it will be appreciated that reactant B exposurephase 140A may have any suitable duration. In some embodiments, reactantB exposure phase 140A may have a duration exceeding a substrate surfacesaturation time for reactant B. For example, the embodiment shown inFIG. 1A depicts a reactant B post-saturation exposure time 150 includedin reactant B exposure phase 140A. Optionally, reactant B exposure phase140A may include a controlled flow of a suitable inert gas, which, asdescribed above, may assist with pressure and/or temperature control ofthe process station, evaporation of a liquid precursor, more rapiddelivery of the precursor and may prevent back-diffusion of processstation gases.

While the CFD process embodiment depicted in FIG. 1A is plasmaactivated, it will be appreciated that other non-thermal energy sourcesmay be used within the scope of the present disclosure. Non-limitingexamples of non-thermal energy sources include, but are not limited to,ultraviolet lamps, downstream or remote plasma sources, capacitivelycoupled plasmas, inductively-coupled plasmas, and microwave surface waveplasmas.

In some scenarios, surface adsorbed B species may exist as discontinuousislands on the substrate surface, making it difficult to achieve surfacesaturation of reactant B. Various surface conditions may delaynucleation and saturation of reactant B on the substrate surface. Forexample, ligands released on adsorption of reactants A and/or B mayblock some surface active sites, preventing further adsorption ofreactant B. Accordingly, in some embodiments, continuous adlayers ofreactant B may be provided by modulating a flow of and/or discretelypulsing reactant B into the process station during reactant B exposurephase 140A. This may provide extra time for surface adsorption anddesorption processes while conserving reactant B compared to a constantflow scenario.

Additionally or alternatively, in some embodiments, one or more sweepphases may be included between consecutive exposures of reactant B. Forexample, the embodiment of FIG. 1B schematically shows an example CFDprocess timing diagram 200 for a deposition cycle 210. At reactant Bexposure phase 240A, reactant B is exposed to the substrate surface.Subsequently, at sweep phase 260A, reactant B is turned off, and gasphase species of reactant B are removed from the process station. In onescenario, gas phase reactant B may be displaced by a continuous flow ofreactant A and/or the inert gas. In another scenario, gas phase reactantB may be removed by evacuating the process station. Removal of gas phasereactant B may shift an adsorption/desorption process equilibrium,desorbing ligands, promoting surface rearrangement of adsorbed B tomerge discontinuous islands of adsorbed B. At reactant B exposure phase240B, reactant B is again exposed to the substrate surface. While theembodiment shown in FIG. 1B includes one instance of a reactant B sweepand exposure cycle, it will be appreciated that any suitable number ofiterations of alternating sweep and exposure cycles may be employedwithin the scope of the present disclosure.

Returning to the embodiment of FIG. 1A, prior to activation by theplasma at 180A, gas phase reactant B may be removed from the processstation in sweep phase 160A in some embodiments. A CFD cycle may includeone or more sweep phases in addition to the above-described exposurephases. Sweeping the process station may avoid gas phase reactions wherereactant B is susceptible to plasma activation. Further, sweeping theprocess station may remove surface adsorbed ligands that may otherwiseremain and contaminate the film. Examples sweep gases include, but arenot limited to, argon, helium, and nitrogen. In the embodiment shown inFIG. 1A, sweep gas for sweep phase 160A is supplied by the inert gasstream. In some embodiments, sweep phase 160A may include one or moreevacuation subphases for evacuating the process station. Alternatively,it will be appreciated that sweep phase 160A may be omitted in someembodiments.

Sweep phase 160A may have any suitable duration. In some embodiments,increasing a flow rate of a one or more sweep gases may decrease theduration of sweep phase 160A. For example, a sweep gas flow rate may beadjusted according to various reactant thermodynamic characteristicsand/or geometric characteristics of the process station and/or processstation plumbing for modifying the duration of sweep phase 160A. In onenon-limiting example, the duration of a sweep phase may be optimized byadjustment of the sweep gas flow rate. This may reduce deposition cycletime, which may improve substrate throughput.

A CFD cycle typically includes an “activation phase” in addition to theexposure and optional sweep phases described above. The activation phaseserves to drive the reaction of the one or more reactants adsorbed onthe substrate surface. At plasma activation phase 180A of the embodimentshown in FIG. 1A, plasma energy is provided to activate surfacereactions between surface adsorbed reactants A and B. For example, theplasma may directly or indirectly activate gas phase molecules ofreactant A to form reactant A radicals. These radicals may then interactwith surface adsorbed reactant B, resulting in film-forming surfacereactions. Plasma activation phase 180A concludes deposition cycle 110A,which in the embodiment of FIG. 1A is followed by deposition cycle 110B,commencing with reactant A exposure phase 120B.

In some embodiments, the plasma ignited in plasma activation phase 180Amay be formed directly above the substrate surface. This may provide agreater plasma density and enhanced surface reaction rate betweenreactants A and B. For example, plasmas for CFD processes may begenerated by applying a radio frequency (RF) field to a low-pressure gasusing two capacitively coupled plates. In alternative embodiments, aremotely generated plasma may be generated outside of the main reactionchamber.

Any suitable gas may be used to form the plasma. In a first example, andinert gas such as argon or helium may be used to form the plasma. In asecond example, a reactant gas such as oxygen or ammonia may be used toform the plasma. In a third example, a sweep gas such as nitrogen may beused to form the plasma. Of course, combinations of these categories ofgases may be employed. Ionization of the gas between the plates by theRF field ignites the plasma, creating free electrons in the plasmadischarge region. These electrons are accelerated by the RF field andmay collide with gas phase reactant molecules. Collision of theseelectrons with reactant molecules may form radical species thatparticipate in the deposition process. It will be appreciated that theRF field may be coupled via any suitable electrodes. Non-limitingexamples of electrodes include process gas distribution showerheads andsubstrate support pedestals. It will be appreciated that plasmas for CFDprocesses may be formed by one or more suitable methods other thancapacitive coupling of an RF field to a gas.

Plasma activation phase 180A may have any suitable duration. In someembodiments, plasma activation phase 180A may have a duration thatexceeds a time for plasma-activated radicals to interact with allexposed substrate surfaces and adsorbates, forming a continuous filmatop the substrate surface. For example, the embodiment shown in FIG. 1Aincludes a plasma post-saturation exposure time 190 in plasma activationphase 180A.

In one scenario, a CFD process may deposit a conformal silicon dioxidefilm on a non-planar substrate. For example, a CFD silicon dioxide filmmay be used for gap fill of structures, such as a trench fill of shallowtrench isolation (STI) structures. While the various embodimentsdescribed below relate to a gap fill application, it will be appreciatedthat this is merely a non-limiting, illustrative application, and thatother suitable applications, utilizing other suitable film materials,may be within the scope of the present disclosure. Other applicationsfor CFD silicon dioxide films include, but are not limited to,interlayer dielectric (ILD) applications, intermetal dielectric (IMD)applications, pre-metal dielectric (PMD) applications, dielectric linersfor through-silicon via (TSV) applications, resistive RAM (ReRAM)applications, and/or stacked capacitor fabrication in DRAM applications.

Doped silicon oxide may be used as a diffusion source for boron,phosphorus, or even arsenic dopants. For example, a boron doped silicateglass (BSG), a phosphorus doped silicate glass (PSG), or even a boronphosphorus doped silicate glass (BPSG) could be used. Doped CFD layerscan be employed to provide conformal doping in, for example,three-dimensional transistor structures such as multi-gate FinFET's andthree-dimensional memory devices. Conventional ion implanters cannoteasily dope sidewalls, especially in high aspect ratio structures.

CFD doped oxides as diffusion sources have various advantages. First,they provide high conformality at low temperature. In comparison,low-pressure CVD produced doped TEOS (tetraethylorthosilicate) is knownbut requires deposition at high temperature, and sub-atmospheric CVD andPECVD doped oxide films are possible at lower temperature but haveinadequate conformality. Conformality of doping is important, but so isconformality of the film itself, since the film typically is asacrificial application and will then need to be removed. Anon-conformal film typically faces more challenges in removal, i.e. someareas can be overetched.

Additionally, CFD provides extremely well controlled dopingconcentration. As mentioned, a CFD process can provide from a few layersof undoped oxide followed by a single layer of doping. The level ofdoping can be tightly controlled by the frequency with which the dopedlayer is deposited and the conditions of the doping cycle. In certainembodiments, the doping cycle is controlled by for instance using adopant source with significant steric hindrance. In addition toconventional silicon-based microelectronics, other applications of CFDdoping include microelectronics and optoelectronics based on III-Vsemiconductors such as GaAs and II-VI semiconductors such as HgCdTe,photovoltaics, flat panel displays, and electrochromic technology.

In some embodiments, a plasma generator may be controlled to provideintermittent pulses of plasma energy during a plasma activation phase.For example, the plasma may be pulsed at one or more frequenciesincluding, but not limited to, frequencies between of 10 Hz and 500 Hz.This may enhance step coverage by reducing a directionality of ionbombardment in comparison to a continuous plasma. Further, this mayreduce ion bombardment damage to the substrate. For example, photoresistsubstrates may be eroded by ion bombardment during a continuous plasma.Pulsing the plasma energy may reduce photoresist erosion.

Concurrent PECVD-type and CFD-type reactions may occur where reactant Bco-exists with reactant A in a plasma environment. In some embodiments,co-existence of reactants in a plasma environment may result from apersistence of reactant B in a process station after a supply ofreactant B has been discontinued, continuing an exposure of reactant Bto the substrate. For example, FIG. 1C shows a timing diagram 2900 foran embodiment of a CFD process including a sweep phase having a positivetime duration between discontinuing a supply of reactant B to theprocess station and plasma activation. As another example, FIG. 1D showsanother timing diagram 3000 for an embodiment of a CFD process excludinga sweep phase (e.g., having a sweep time=0) between discontinuing asupply of reactant B and plasma activation.

In some embodiments, co-existence of reactants in a plasma environmentmay result from concurrent supply of reactant B to the process stationand plasma activation. For example, FIG. 1E shows a timing diagram 3100for an embodiment of a CFD process having an overlap (indicated by a“negative” sweep time) between a supply of reactant B to the processstation and plasma activation.

While the various CFD deposition processes described above have beendirected at depositing, treating, and/or etching single film types, itwill be appreciated that some CFD processes within the scope of thepresent disclosure may include in-situ deposition of a plurality of filmtypes. For example, alternating layers of film types may be depositedin-situ. In a first scenario, a double spacer for a gate device may befabricated by in-situ deposition of a silicon nitride/silicon oxidespacer stack. This may reduce cycle time and increase process stationthroughput, and may avoid interlayer defects formed by potential filmlayer incompatibility. In a second scenario, an antireflective layer forlithographic patterning applications may be deposited as a stack of SiONor amorphous silicon and SiOC with tunable optical properties. Inanother scenario, a protective film layer is first deposited on asensitive substrate (e.g., at the low damage conditions describedherein), and then an electrically favorable film layer is deposited onthe protective film layer. This bilayer approach may be used to preventoxidation, nitridation, or other reaction on a sensitive substrate.

Many different reactants may be used in practicing the disclosedembodiments. Where the film deposited includes silicon, the siliconcompound can be, for example, a silane, a halosilane or an aminosilane.A silane contains hydrogen and/or carbon groups, but does not contain ahalogen. Examples of silanes are silane (SiH₄), disilane (Si₂H₆), andorgano silanes such as methylsilane, ethylsilane, isopropylsilane,t-butylsilane, dimethylsilane, diethylsilane, di-t-butyl silane,allylsilane, sec-butyl silane, thexylsilane, isoamylsilane,t-butyldisilane, di-t-butyldisilane, and the like. A halosilane containsat least one halogen group and may or may not contain hydrogens and/orcarbon groups. Examples of halosilanes are iodosilanes, bromosilanes,chlorosilanes and fluorosilanes. Although halosilanes, particularlyfluorosilanes, may form reactive halide species that can etch siliconmaterials, in certain embodiments described herein, thesilicon-containing reactant is not present when a plasma is struck.Specific chlorosilanes are tetrachlorosilane (SiCl₄), trichlorosilane(HSiCl₃), dichlorosilane (H₂SiCl₂), monochlorosilane (ClSiH₃),chloroallylsilane, chloromethylsilane, dichloromethylsilane,chlorodimethylsilane, chloroethylsilane, t-butylchlorosilane,di-t-butylchlorosilane, chloroisopropylsilane, chloro-sec-butylsilane,t-butyldimethylchlorosilane, thexyldimethylchlorosilane, and the like.An aminosilane includes at least one nitrogen atom bonded to a siliconatom, but may also contain hydrogens, oxygens, halogens and carbons.Examples of aminosilanes are mono-, di-, tri- and tetra-aminosilane(H₃Si(NH₂)₄, H₂Si(NH₂)₂, HSi(NH₂)₃ and Si(NH₂)₄, respectively), as wellas substituted mono-, di-, tri- and tetra-aminosilanes, for example,t-butylaminosilane, methylaminosilane, tert-butylsilanamine,bis(tertiarybutylamino)silane (SiH₂(NHC(CH₃)₃)₂ (BTBAS), tert-butylsilylcarbamate, SiH(CH₃)—(N(CH₃)₂)₂, SiHCl—(N(CH₃)₂)₂, (Si(CH₃)₂NH)₃,bisdiethylaminosilane (BDEAS), diisopropylaminosilane (DIPAS),tridimethylaminotitanium (TDMAT), and the like. A further example of anaminosilane is trisilylamine (N(SiH₃)₃).

In other cases, the deposited film contains metal. Examples ofmetal-containing films that may be formed include oxides and nitrides ofaluminum, titanium, hafnium, tantalum, tungsten, manganese, magnesium,strontium, etc., as well as elemental metal films. Example precursorsmay include metal alkylamines, metal alkoxides, metal alkylamides, metalhalides, metal ß-diketonates, metal carbonyls, organometallics, etc.Appropriate metal-containing precursors will include the metal that isdesired to be incorporated into the film. For example, atantalum-containing layer may be deposited by reactingpentakis(dimethylamido)tantalum with ammonia or another reducing agent.Further examples of metal-containing precursors that may be employedinclude trimethylaluminum, tetraethoxytitanium, tetrakis-dimethyl-amidotitanium, hafnium tetrakis(ethylmethylamide),bis(cyclopentadienyl)manganese, andbis(n-propylcyclopentadienyl)magnesium.

In some embodiments, the deposited film contains nitrogen, and anitrogen-containing reactant must be used. A nitrogen-containingreactant contains at least one nitrogen, for example, ammonia,hydrazine, amines (e.g., amines bearing carbon) such as methylamine,dimethylamine, ethylamine, isopropylamine, t-butylamine,di-t-butylamine, cyclopropylamine, sec-butylamine, cyclobutylamine,isoamylamine, 2-methylbutan-2-amine, trimethylamine, diisopropylamine,diethylisopropylamine, di-t-butylhydrazine, as well as aromaticcontaining amines such as anilines, pyridines, and benzylamines. Aminesmay be primary, secondary, tertiary or quaternary (for example,tetraalkylammonium compounds). A nitrogen-containing reactant cancontain heteroatoms other than nitrogen, for example, hydroxylamine,t-butyloxycarbonyl amine and N-t-butyl hydroxylamine arenitrogen-containing reactants.

In certain implementations, an oxygen-containing oxidizing reactant isused. Examples of oxygen-containing oxidizing reactants include oxygen,ozone, nitrous oxide, nitric oxide, nitrogen dioxide, carbon monoxide,carbon dioxide, sulfur monoxide, sulfur dioxide, oxygen-containinghydrocarbons (C_(x)H_(y)O_(z)), water (H₂O), mixtures thereof, etc.

In some embodiments, an optional pumpdown to less than about 1 Torr(e.g., using a setpoint of 0) may be employed after the plasma isextinguished, either before, during or after a post-plasma purge, ifperformed.

As mentioned above, conventional methods of depositing oxides can resultin damage to the underlying substrate. FIG. 2 shows the existence ofoxidation-related damage to the underlying substrate as occurs in a CFDmethod of depositing a silicon oxide layer at T=400° C. and RF Power=625W/station using an N₂/O₂ oxidizer. By using a linear fit for filmthickness (CFDOx Thickness) vs. number of CFD cycles, the y-interceptprovides information regarding the native oxide thickness on thesubstrate surface. A y-intercept of zero would indicate that there wasno oxidation of the underlying substrate during the deposition. As shownin FIG. 2, however, the method results in a native oxidation thicknessof approximately 0.6 nm or 6 Å.

There are several critical factors which affect the amount of oxidationon sensitive substrates. Such factors include the temperature of thesubstrate during the deposition process, the power used to ignite theplasma, the choice of oxidation reactant, the chamber pressure, and thelength of time that plasma power is applied during the depositionprocess. In various cases, a protective layer can be formed bymaintaining the substrate between about 25° C. and 450° C. Generally,lower substrate temperatures will result in less oxidation of thesubstrate. In some embodiments, the protective layer can be formed bymaintaining the substrate between about 25° C. and 200° C., for examplebetween about 50° C. and 150° C. However, temperatures as high as 450°C. or even higher may be used in certain embodiments if other conditionssuch as plasma power are adjusted.

Another critical factor affecting the level of substrate oxidation isthe power used to ignite the plasma during the CFD process. Lower powerresults in less oxidation of the substrate. FIG. 3A shows the effect ofRF power on the thickness of the oxidation of the substrate in a CFDdeposition using N₂O as the oxidant at 2.5 Torr. RF values compared herewere 500 W (shown in diamonds), 350 W (shown in squares), 250 W (shownin triangles), and 250 W at 3×RF time (shown in X's). In FIG. 3A, as inFIG. 2, the y-intercept represents the amount of substrate oxidation.Thus, it can be seen that higher values of RF power have largery-intercepts, and correspondingly higher levels of substrate oxidation.In FIGS. 3A and 3B (discussed further below) as well as in Table 1,below, the RF levels reported represent the total RF power used. Thistotal power was divided between 4 RF stations. The RF power onset valuefor oxidation may be between about 60-90 W/station. An RF power value of62.5 W/station exhibited almost no oxidation of the substrate.Accordingly, in certain embodiments, plasma-enhanced deposition may beperformed at no more than about 60-90 W per station on anoxidation-sensitive substrate, below the RF power onset value foroxidation.

Table 1 below, which corresponds to the conditions and data shown inFIG. 3A, illustrates that the film stress may be modulated by varyingthe RF flux (i.e., RF power and/or RF time). At higher RF powers such asaround 4 kW, the stress is about −200 to −250 MPa compressive. At thelower RF powers shown here, the stress becomes less compressive andcloser to neutral. Table 1 also indicates that shorter RF times atequivalent RF power values also result in more neutral stress values.For example, where the RF power is 250 W, increasing the RF time by afactor of three raises the film stress by about a factor of three.Increasing the RF time also results in an increase in the breakdownvoltage of the film (i.e., the BDV becomes more negative). This suggeststhat films formed at the low damage conditions may suffer from lowbreakdown voltages. However, this may not always be the case, evidencedby the fact that the film formed at 500 W showed a BDV lower (lessnegative) than the film formed at 250 W.

TABLE 1 Protective Layer ALD Film Properties with Different RF power andRF time Within- Wafer Condition Non- Thickness (N2O only, Thicknessuniformity Range Stress Dep. Rate BDV 2.5 T) (A) (%) (A) (MPa) (A/cycle)(MV/cm) 250 W 1309 0.70 23 −16 1.19 −1.3 250 W at 1552 0.17 14 −45 1.41−1.7 3xRF time 500 W 1454 0.17 15 −46 1.32 −1.2

All RF levels provided herein are for 300 mm wafers and may be scaledappropriately for wafers of different sizes. The RF power levels scalelinearly with wafer area (conversion of RF power levels for wafers ofother sizes may be done by maintaining the plasma density anddistribution per unit area constant). For example, a reported value of125 W/station may be scaled to approximately 280 W/station for a 450 mmdiameter wafer.

In one embodiment, the RF power used to create the protective layer isbetween about 12.5 and 125 W/station. In another embodiment, the RFpower used to create the protective layer is between about 50 and 125W/station, or below about 100 W/station.

The amount of time over which the RF power is applied (RF time) can alsoaffect the amount of substrate oxidation. Generally, longer RF timeswill result in more oxidation of the substrate. The duration of RF timeduring an plasma-enhanced ALD or CFD cycle may range from about 50 ms toabout 1 s, for example about 0.25 s.

The RF levels described herein refer to high-frequency (HF) RF, thoughin certain embodiments, low frequency (LF) RF may be applied in additionto HF RF. Example high-frequency RF frequencies may include, but are notlimited to, frequencies between about 1.8 MHz and 2.45 GHz. Examplelow-frequency RF frequencies may include, but are not limited to,frequencies between about 50 kHz and 500 kHz.

The choice of oxidation reactant can also affect the amount of substrateoxidation. The oxidation reactant is often a mixture of O₂ and a weakoxidizer. Examples of weak oxidizers include carbon oxides such ascarbon dioxide (CO₂) and carbon monoxide (CO), nitrogen oxides such asnitrous oxide (N₂O), nitric oxide (NO) and nitrogen dioxide (NO₂), andsulfur oxides such as sulfur oxide (SO) and sulfur dioxide (SO₂).Examples of other weak oxidizers include any oxygen containinghydrocarbons (C_(x)HyO_(z)) and water (H₂O). Generally, lower relativeamounts of O₂ and higher relative amounts of weak oxidizer result inless oxidation of the substrate. In some cases, the O₂ may be eliminatedfrom the oxidation reactant altogether. In some embodiments, theoxidation reactant may include ozone in addition to or in place of aweak oxidizer. While ozone is generally a strong oxidizer, surfacereactions such as those occurring during CFD may not be ion-driven, thusmaking ozone a potential candidate for the oxidation reactant, or aningredient therein. Where ozone is used, surface damage to the substratemay be limited to the radical reaction enabled by the singlet state.Conversely, cracking of O₂ with plasma (e.g., a capacitively coupled orinductively coupled plasma) may impart ion related damage to thesubstrate due to the presence of O⁻.

FIG. 3B demonstrates the effect of using two different oxidationreactants. The data are shown at two different levels of RF power. Theamount of substrate oxidation decreases when the oxidation reactant issolely N₂O, as compared to when the oxidation reactant is a mixture ofN₂O and O₂.

In one embodiment for forming a protective film on a sensitivesubstrate, the oxidation reactant is between 0 and about 50% O₂, andbetween about 50 and 100% weak oxidizer. The oxidation reactant may bebetween 0 and 50% O₂, with the balance one or more weak oxidizers. Therate of oxidation reactant flow can range from about 1-25 SLM total. Forexample, the oxidation reactant may flow at about 20 SLM total, withabout 10 SLM O₂ and about 10 SLM weak oxidizer such as N₂O. Theoxidation reactant may be introduced coincident with the RF strike ormay flow continuously.

In some embodiments, a silicon-containing reactant is used. Thisreactant may be introduced at a rate between about 0.25 mL/min and about4 mL/min, and in some embodiments is introduced at a rate of about 0.5mL/min.

Although much of the description in this document focuses on formationof silicon oxide films, the methods described herein may also be used toform other types of films on reaction-sensitive substrates. For example,the temperatures and RF power levels described above may be used to formSiN in a plasma-assisted reaction using a silicon precursor and anitrogen-containing co-reactant. In this manner, unwanted nitridation ofnitridation-sensitive substrates can be prevented. Moreover, the methodsmay also be used with deposition of non-silicon containing filmsincluding metal oxide and metal nitride films.

Another important factor affecting substrate oxidation is the pressureat which the CFD process occurs. Lower pressures may lead to lessoxidation, making it preferable to run the CFD process at a low pressurewhile creating the protective layer. In one embodiment, the pressure maybe between about 2 to 10 Torr, for example about 6 Torr.

The thickness of the protective layer is an important characteristicwith respect to the performance of the resulting product. The processingconditions used to manufacture the protective layer may result in poorelectrical qualities in the film. Thus, the protective layer should bethick enough to adequately prevent oxidation of the underlying substrateduring subsequent processing and use, while being thin enough to achievethe overall desired electrical properties of the film. In oneembodiment, the protective layer may range from about 10 to about 50 Åthick. While 50 Å may be sufficient to prevent subsequent oxidationduring more aggressive process conditions, in some embodiments theprotective layer may be thicker, for example less than about 100 Å, orin some cases even greater than 100 Å. In some embodiments, theprotective layer may be the entire SiO₂ (or other material) layer.

In one aspect of the invention, the protective layer is incorporatedinto a bilayer. The protective layer forms the bottom layer, and anelectrically favorable layer is deposited on top of the protectivelayer. Because the protective layer may have electrically unfavorablequalities such as low breakdown voltage (BDV) and high leakage currentdue to insufficient oxidative conversion, it is desirable to deposit theelectrically favorable layer on top, thereby ensuring that the resultingproduct has the desired electrical qualities. The electrically favorablelayer may be deposited at a higher substrate temperature, a higher RFpower, a higher pressure, a longer RF time, and/or using a differentoxidation (or other auxiliary) reactant than those used for producingthe bottom protective layer.

In forming the electrically favorable layer, the substrate temperatureis generally kept between about 50° C. and about 400° C. In someembodiments, the substrate is kept between about 150° C. and about 250°C., and in other embodiments the substrate is kept between about 300° C.and about 400° C. While in some embodiments the formation of each layeroccurs at the same substrate temperature (i.e., the bilayer is createdisothermally), in other embodiments the substrate temperature is higherduring formation of the electrically favorable layer.

The RF power level used to create the electrically favorable layer mayrange from about 62.5 W/station to about 375 W/station, for example 250W/station. The RF time may range from about 50 ms to about 1 s, and inone embodiment is about 0.25 s.

Like the oxidation reactant used to create the protective layer, theoxidation reactant used to create the electrically favorable layer isusually a mix of O₂ and weak oxidizer containing between 0 and about 50%O₂ and 50-100% weak oxidizer. In some embodiments, the ratio of O₂:weakoxidizer is higher during the deposition of the electrically favorablelayer compared to the ratio used for deposition of the protective layer.In other embodiments, the same ratio of O₂:weak oxidizer is used for thedeposition of each layer. The total flow of oxidation reactant may rangefrom about 1-25 SLM, and in one embodiment is about 20 SLM with about 10SLM O₂ and about 10 SLM weak oxidizer such as N₂O.

In some embodiments, a silicon-containing reactant is used to depositthe electrically favorable layer. This reactant may be introduced at arate between about 0.25 mL/min and about 4 mL/min, and in someembodiments is introduced at a rate of about 0.5 mL/min.

The pressure used to create the electrically favorable layer may rangefrom about 2 to about 10 Torr, for example about 6 Torr. In someembodiments, the protective layer and the electrically favorable layerare each deposited at the same pressure, while in other embodiments theelectrically favorable layer is deposited at a relatively higherpressure to achieve the desired electrical qualities.

The thickness of the electrically favorable layer is governed by theapplication for which it will be used. For example, the layer may bebetween about 1 nm and about 25 nm for caps in logic technology, whereasthe layer may be between about 5 Å-40 Å for interfacial layers in logictechnology. Other thicknesses may be appropriate in different contexts.

Another characteristic that is important to the functionality of theresulting product is the relative thicknesses of the protective andelectrically favorable layers. In some embodiments, the protective layeris between about 1% and about 20% of the total thickness of the bilayer.Some applications may require proportions which fall outside this range,for example less than 1% or greater than 20% of the total thickness.

FIG. 4 shows the breakdown voltage (BDV) for a range of relativethicknesses of the protective layer. All film thicknesses for this dataset were 1000±50 Å. Data points that are further to the right on thex-axis in FIG. 4 represent bilayers having relatively thicker protectivefilms and relatively thinner electrically favorable films. The processfor forming the electrically favorable layer was run at T=150° C., HFPower=625 W/station, 3.5 T, using an O₂/N₂O oxidizer reactant. Theprocess for forming the protective layer was run at T=150° C., HFpower=65 W/station, 2.5 T, using N₂O as an oxidizer reactant. The BDV ofthe bilayer shows a strong dependence on the relative thickness of theprotective layer in the bilayer, showing that the bilayer film stack'selectrical properties are tunable. The data suggest that the BDV isstill relatively good when the protective layer is around or less thanabout 20% of the total thickness of the bilayer.

Another aspect of the present invention is a method to evaluatesubstrate oxidation using a regular silicon substrate as the testvehicle, thereby avoiding the complexity of testing oxidation on devicesubstrates. The method involves running the CFD process through manycycles and plotting the thickness of the layer vs. the number of cycles.By using a linear fit between the variables (thereby assuming that eachCFD cycle deposits approximately the same thickness of film), they-intercept can be extrapolated to provide the native oxide thickness onthe substrate surface. A higher y-intercept implies more oxidation ofthe substrate, while a y-intercept of zero would imply that there was nooxidation of the substrate. An example of this method is described inrelation to FIG. 2, above. When practicing this method, a number of filmlayers should be deposited before taking the first thicknessmeasurement. This may help provide more accurate information regardingthe damage to the substrate. In some implementations, at least about 5,or at least about 10 layers are deposited before the first thicknessmeasurement is taken. After the substrate is coated during a nucleationphase of deposition, the substrate damage is expected to be minimal.

Another aspect of the invention relates to a method to determine theminimal thickness of the protective layer in the bilayer approachdescribed above. This method will allow choice of a protective layerthickness that is sufficiently thick to protect the oxidation-sensitivesubstrate, while not being so thick as to detrimentally affect thedesired electrical properties of the bilayer.

A series of protective film layers of different thicknesses can bedeposited on individual substrates including, but not limited to,silicon wafers. For example, layers of different thicknesses rangingfrom about 0 Å to about 300 Å are deposited on individual substrates.The pre-plasma thickness of the layer on each substrate is measured.Next, the film layers are each exposed to 100 cycles of non-depositionplasma. For example, a substrate can be exposed to non-deposition cyclesof a mixture of O₂/N₂O plasma with RF power=2500 W (625 W/station),substrate temperature=150° C., and P=3.5 T. Next, the post-plasmathickness of each layer is measured. Δthickness is calculated as thedifference between the pre-plasma thickness and the post-plasmathickness. The Δthickness is plotted against the pre-plasma thickness ofthe film layers. The minimal thickness used to protect the substratefrom oxidation can be determined by finding the thickness at which theΔthickness is saturated (i.e., where the Δthickness levels out orbecomes substantially stable). Substantially stable may mean when oneadditional layer of film results in a change in Δthickness of less thanabout 0.5 Å. At this point, the increase in thickness due to surfaceoxidation is prevented by the protective film and the Δthickness resultspurely from the contribution of film densification by plasma ionbombardment

The above analysis assumes that Δthickness has two major contributors:(1) an increase in thickness due to substrate oxidation caused by Ospecies penetrating through the protective layer, and (2) a decrease inthickness due to film densification by plasma ion bombardment. Becauseeach wafer is processed with the same RF cycles, the film densificationis assumed to be uniform across the different wafers.

FIG. 5 shows a set of experimental data obtained using this method. Asseen in FIG. 5, the data suggest that substrate oxidation waseffectively prevented by a 50-100 Å thick protective layer. Furthermore,the data also suggest that the film densification caused by 100 cyclesat the conditions described above resulted in a film densification ofapproximately 5 Å. Where other deposition conditions are used (e.g.,different film types, underlying substrates, RF flux, temperature,pressure, etc.), the minimum thickness may be different. The disclosedmethod may be used to tailor a specific bilayer formation process toachieve the necessary electrical characteristics.

The numbers used in describing this method are given by way of exampleonly, and are not intended to limit the scope of the invention. One ofordinary skill in the art would understand that a broad range oftemperatures, RF powers, pressures and plasma compositions may be used.

Apparatus

It will be appreciated that any suitable process station may be employedwith one or more of the embodiments described above. For example, FIG. 6schematically shows an embodiment of a CFD process station 1300. Forsimplicity, CFD process station 1300 is depicted as a standalone processstation having a process chamber body 1302 for maintaining alow-pressure environment. However, it will be appreciated that aplurality of CFD process stations 1300 may be included in a commonprocess tool environment. For example, FIG. 7 depicts an embodiment of amulti-station processing tool 2400. Further, it will be appreciatedthat, in some embodiments, one or more hardware parameters of CFDprocess station 1300, including those discussed in detail above, may beadjusted programmatically by one or more computer controllers.

CFD process station 1300 fluidly communicates with reactant deliverysystem 1301 for delivering process gases to a distribution showerhead1306. Reactant delivery system 1301 includes a mixing vessel 1304 forblending and/or conditioning process gases for delivery to showerhead1306. One or more mixing vessel inlet valves 1320 may controlintroduction of process gases to mixing vessel 1304.

Some reactants, like BTBAS, may be stored in liquid form prior tovaporization at and subsequent delivery to the process station. Forexample, the embodiment of FIG. 6 includes a vaporization point 1303 forvaporizing liquid reactant to be supplied to mixing vessel 1304. In someembodiments, vaporization point 1303 may be a heated vaporizer. Thesaturated reactant vapor produced from such vaporizers may condense indownstream delivery piping. Exposure of incompatible gases to thecondensed reactant may create small particles. These small particles mayclog piping, impede valve operation, contaminate substrates, etc. Someapproaches to addressing these issues involve sweeping and/or evacuatingthe delivery piping to remove residual reactant. However, sweeping thedelivery piping may increase process station cycle time, degradingprocess station throughput. Thus, in some embodiments, delivery pipingdownstream of vaporization point 1303 may be heat traced. In someexamples, mixing vessel 1304 may also be heat traced. In onenon-limiting example, piping downstream of vaporization point 1303 hasan increasing temperature profile extending from approximately 100degrees Celsius to approximately 150 degrees Celsius at mixing vessel1304.

In some embodiments, reactant liquid may be vaporized at a liquidinjector. For example, a liquid injector may inject pulses of a liquidreactant into a carrier gas stream upstream of the mixing vessel. In onescenario, a liquid injector may vaporize reactant by flashing the liquidfrom a higher pressure to a lower pressure. In another scenario, aliquid injector may atomize the liquid into dispersed microdroplets thatare subsequently vaporized in a heated delivery pipe. It will beappreciated that smaller droplets may vaporize faster than largerdroplets, reducing a delay between liquid injection and completevaporization. Faster vaporization may reduce a length of pipingdownstream from vaporization point 1303. In one scenario, a liquidinjector may be mounted directly to mixing vessel 1304. In anotherscenario, a liquid injector may be mounted directly to showerhead 1306.

In some embodiments, a liquid flow controller upstream of vaporizationpoint 1303 may be provided for controlling a mass flow of liquid forvaporization and delivery to process station 1300. For example, theliquid flow controller (LFC) may include a thermal mass flow meter (MFM)located downstream of the LFC. A plunger valve of the LFC may then beadjusted responsive to feedback control signals provided by aproportional-integral-derivative (PID) controller in electricalcommunication with the MFM. However, it may take one second or more tostabilize liquid flow using feedback control. This may extend a time fordosing a liquid reactant. Thus, in some embodiments, the LFC may bedynamically switched between a feedback control mode and a directcontrol mode. In some embodiments, the LFC may be dynamically switchedfrom a feedback control mode to a direct control mode by disabling asense tube of the LFC and the PID controller.

Showerhead 1306 distributes process gases toward substrate 1312. In theembodiment shown in FIG. 6, substrate 1312 is located beneath showerhead1306, and is shown resting on a pedestal 1308. It will be appreciatedthat showerhead 1306 may have any suitable shape, and may have anysuitable number and arrangement of ports for distributing processesgases to substrate 1312.

In some embodiments, a microvolume 1307 is located beneath showerhead1306. Performing a CFD process in a microvolume rather than in theentire volume of a process station may reduce reactant exposure andsweep times, may reduce times for altering CFD process conditions (e.g.,pressure, temperature, etc.), may limit an exposure of process stationrobotics to process gases, etc. Example microvolume sizes include, butare not limited to, volumes between 0.1 liter and 2 liters.

In some embodiments, pedestal 1308 may be raised or lowered to exposesubstrate 1312 to microvolume 1307 and/or to vary a volume ofmicrovolume 1307. For example, in a substrate transfer phase, pedestal1308 may be lowered to allow substrate 1312 to be loaded onto pedestal1308. During a CFD process phase, pedestal 1308 may be raised toposition substrate 1312 within microvolume 1307. In some embodiments,microvolume 1307 may completely enclose substrate 1312 as well as aportion of pedestal 1308 to create a region of high flow impedanceduring a CFD process.

Optionally, pedestal 1308 may be lowered and/or raised during portionsthe CFD process to modulate process pressure, reactant concentration,etc., within microvolume 1307. In one scenario where process chamberbody 1302 remains at a base pressure during the CFD process, loweringpedestal 1308 may allow microvolume 1307 to be evacuated. Example ratiosof microvolume to process chamber volume include, but are not limitedto, volume ratios between 1:500 and 1:10. It will be appreciated that,in some embodiments, pedestal height may be adjusted programmatically bya suitable computer controller.

In another scenario, adjusting a height of pedestal 1308 may allow aplasma density to be varied during plasma activation and/or treatmentcycles included in the CFD process. At the conclusion of the CFD processphase, pedestal 1308 may be lowered during another substrate transferphase to allow removal of substrate 1312 from pedestal 1308.

In some embodiments, the pedestal 1308 may be cooled to help preventdamage to a substrate during a deposition process. Other portions of theapparatus/hardware may also be cooled to help reduce damage to thesubstrate. For instance, a cooled showerhead and/or a cooled chamber maybe used. Examples of chamber surfaces that may be cooled include a topplate, chamber body, ribs, filler plates, spindle, transfer arm, etc.The cooling may counteract a raise in temperature that may otherwiseoccur. One purpose of the cooling is to maintain the substrate at alower temperature. The temperature of these cooled components may be inthe range of about 25-300° C., or between about 35-100° C. The coolingmay be accomplished by providing a cooling loop that circulates liquidfrom a chiller, for example. Other cooling methods may also be used, andare generally known by those of ordinary skill in the art.

While the example microvolume variations described herein refer to aheight-adjustable pedestal, it will be appreciated that, in someembodiments, a position of showerhead 1306 may be adjusted relative topedestal 1308 to vary a volume of microvolume 1307. Further, it will beappreciated that a vertical position of pedestal 1308 and/or showerhead1306 may be varied by any suitable mechanism within the scope of thepresent disclosure. In some embodiments, pedestal 1308 may include arotational axis for rotating an orientation of substrate 1312. It willbe appreciated that, in some embodiments, one or more of these exampleadjustments may be performed programmatically by one or more suitablecomputer controllers.

Returning to the embodiment shown in FIG. 6, showerhead 1306 andpedestal 1308 electrically communicate with RF power supply 1314 andmatching network 1316 for powering a plasma. In some embodiments, theplasma energy may be controlled by controlling one or more of a processstation pressure, a gas concentration, an RF source power, an RF sourcefrequency, and a plasma power pulse timing. For example, RF power supply1314 and matching network 1316 may be operated at any suitable power toform a plasma having a desired composition of radical species. Examplesof suitable powers are included above. Likewise, RF power supply 1314may provide RF power of any suitable frequency. In some embodiments, RFpower supply 1314 may be configured to control high- and low-frequencyRF power sources independently of one another. Example low-frequency RFfrequencies may include, but are not limited to, frequencies between 50kHz and 500 kHz. Example high-frequency RF frequencies may include, butare not limited to, frequencies between 1.8 MHz and 2.45 GHz. It will beappreciated that any suitable parameters may be modulated discretely orcontinuously to provide plasma energy for the surface reactions. In onenon-limiting example, the plasma power may be intermittently pulsed toreduce ion bombardment with the substrate surface relative tocontinuously powered plasmas.

In some embodiments, the plasma may be monitored in-situ by one or moreplasma monitors. In one scenario, plasma power may be monitored by oneor more voltage, current sensors (e.g., VI probes). In another scenario,plasma density and/or process gas concentration may be measured by oneor more optical emission spectroscopy sensors (OES). In someembodiments, one or more plasma parameters may be programmaticallyadjusted based on measurements from such in-situ plasma monitors. Forexample, an OES sensor may be used in a feedback loop for providingprogrammatic control of plasma power. It will be appreciated that, insome embodiments, other monitors may be used to monitor the plasma andother process characteristics. Such monitors may include, but are notlimited to, infrared (IR) monitors, acoustic monitors, and pressuretransducers.

In some embodiments, the plasma may be controlled via input/outputcontrol (IOC) sequencing instructions. In one example, the instructionsfor setting plasma conditions for a plasma activation phase may beincluded in a corresponding plasma activation recipe phase of a CFDprocess recipe. In some cases, process recipe phases may be sequentiallyarranged, so that all instructions for a CFD process phase are executedconcurrently with that process phase. In some embodiments, instructionsfor setting one or more plasma parameters may be included in a recipephase preceding a plasma process phase. For example, a first recipephase may include instructions for setting a flow rate of an inertand/or a reactant gas, instructions for setting a plasma generator to apower set point, and time delay instructions for the first recipe phase.A second, subsequent recipe phase may include instructions for enablingthe plasma generator and time delay instructions for the second recipephase. A third recipe phase may include instructions for disabling theplasma generator and time delay instructions for the third recipe phase.It will be appreciated that these recipe phases may be furthersubdivided and/or iterated in any suitable way within the scope of thepresent disclosure.

In conventional deposition processes, plasma strikes last on the orderof a few seconds or more in duration. In certain implementationsdescribed herein, much shorter plasma strikes may be applied during aCFD cycle. These may be on the order of 50 ms to 1 second, with 0.25seconds being a specific example. Such short RF plasma strikes requirequick stabilization of the plasma. To accomplish this, the plasmagenerator may be configured such that the impedance match is preset to aparticular voltage, while the frequency is allowed to float.Conventionally, high-frequency plasmas are generated at an RF frequencyat about 13.56 MHz. In various embodiments disclosed herein, thefrequency is allowed to float to a value that is different from thisstandard value. By permitting the frequency to float while fixing theimpedance match to a predetermined voltage, the plasma can stabilizemuch more quickly, a result which may be important when using the veryshort plasma strikes associated with CFD cycles.

In some embodiments, pedestal 1308 may be temperature controlled viaheater 1310. Further, in some embodiments, pressure control for CFDprocess station 1300 may be provided by butterfly valve 1318. As shownin the embodiment of FIG. 6, butterfly valve 1318 throttles a vacuumprovided by a downstream vacuum pump (not shown). However, in someembodiments, pressure control of process station 1300 may also beadjusted by varying a flow rate of one or more gases introduced to CFDprocess station 1300.

As described above, one or more process stations may be included in amulti-station processing tool. FIG. 7 shows a schematic view of anembodiment of a multi-station processing tool 2400 with an inbound loadlock 2402 and an outbound load lock 2404, either or both of which maycomprise a remote plasma source. A robot 2406, at atmospheric pressure,is configured to move wafers from a cassette loaded through a pod 2408into inbound load lock 2402 via an atmospheric port 2410. A wafer isplaced by the robot 2406 on a pedestal 2412 in the inbound load lock2402, the atmospheric port 2410 is closed, and the load lock is pumpeddown. Where the inbound load lock 2402 comprises a remote plasma source,the wafer may be exposed to a remote plasma treatment in the load lockprior to being introduced into a processing chamber 2414. Further, thewafer also may be heated in the inbound load lock 2402 as well, forexample, to remove moisture and adsorbed gases. Next, a chambertransport port 2416 to processing chamber 2414 is opened, and anotherrobot (not shown) places the wafer into the reactor on a pedestal of afirst station shown in the reactor for processing. While the embodimentdepicted in FIG. 4 includes load locks, it will be appreciated that, insome embodiments, direct entry of a wafer into a process station may beprovided.

The depicted processing chamber 2414 comprises four process stations,numbered from 1 to 4 in the embodiment shown in FIG. 7. Each station hasa heated pedestal (shown at 2418 for station 1), and gas line inlets. Itwill be appreciated that in some embodiments, each process station mayhave different or multiple purposes. For example, in some embodiments, aprocess station may be switchable between a CFD and PECVD process mode.Additionally or alternatively, in some embodiments, processing chamber2414 may include one or more matched pairs of CFD and PECVD processstations. While the depicted processing chamber 2414 comprises fourstations, it will be understood that a processing chamber according tothe present disclosure may have any suitable number of stations. Forexample, in some embodiments, a processing chamber may have five or morestations, while in other embodiments a processing chamber may have threeor fewer stations.

FIG. 7 also depicts an embodiment of a wafer handling system 2490 fortransferring wafers within processing chamber 2414. In some embodiments,wafer handling system 2490 may transfer wafers between various processstations and/or between a process station and a load lock. It will beappreciated that any suitable wafer handling system may be employed.Non-limiting examples include wafer carousels and wafer handling robots.FIG. 7 also depicts an embodiment of a system controller 2450 employedto control process conditions and hardware states of process tool 2400.System controller 2450 may include one or more memory devices 2456, oneor more mass storage devices 2454, and one or more processors 2452.Processor 2452 may include a CPU or computer, analog and/or digitalinput/output connections, stepper motor controller boards, etc.

In some embodiments, system controller 2450 controls all of theactivities of process tool 2400. System controller 2450 executes systemcontrol software 2458 stored in mass storage device 2454, loaded intomemory device 2456, and executed on processor 2452. System controlsoftware 2458 may include instructions for controlling the timing,mixture of gases, chamber and/or station pressure, chamber and/orstation temperature, wafer temperature, target power levels, RF powerlevels, RF exposure time, substrate pedestal, chuck and/or susceptorposition, and other parameters of a particular process performed byprocess tool 2400. System control software 2458 may be configured in anysuitable way. For example, various process tool component subroutines orcontrol objects may be written to control operation of the process toolcomponents necessary to carry out various process tool processes. Systemcontrol software 2458 may be coded in any suitable computer readableprogramming language.

In some embodiments, system control software 2458 may includeinput/output control (IOC) sequencing instructions for controlling thevarious parameters described above. For example, each phase of a CFDprocess may include one or more instructions for execution by systemcontroller 2450. The instructions for setting process conditions for aCFD process phase may be included in a corresponding CFD recipe phase.In some embodiments, the CFD recipe phases may be sequentially arranged,so that all instructions for a CFD process phase are executedconcurrently with that process phase.

Other computer software and/or programs stored on mass storage device2454 and/or memory device 2456 associated with system controller 2450may be employed in some embodiments. Examples of programs or sections ofprograms for this purpose include a substrate positioning program, aprocess gas control program, a pressure control program, a heatercontrol program, and a plasma control program.

A substrate positioning program may include program code for processtool components that are used to load the substrate onto pedestal 2418and to control the spacing between the substrate and other parts ofprocess tool 2400.

A process gas control program may include code for controlling gascomposition and flow rates and optionally for flowing gas into one ormore process stations prior to deposition in order to stabilize thepressure in the process station. In some embodiments, the controllerincludes instructions for depositing a protective layer at a first setof reactant conditions and instructions for depositing an electricallyfavorable layer at a second set of reactant conditions. The second setof reactant conditions may include a higher ratio of strongoxidizer:weak oxidizer.

A pressure control program may include code for controlling the pressurein the process station by regulating, for example, a throttle valve inthe exhaust system of the process station, a gas flow into the processstation, etc. In some embodiments, the controller includes instructionsfor depositing a protective layer at a first pressure, and depositing anelectrically favorable layer over the protective layer at a secondpressure, where the second pressure is higher than the first pressure.

A heater control program may include code for controlling the current toa heating unit that is used to heat the substrate. Alternatively, theheater control program may control delivery of a heat transfer gas (suchas helium) to the substrate. In certain implementations, the controllerincludes instructions for depositing a protective layer at a firsttemperature, and an electrically favorable layer over the protectivelayer at a second temperature, where the second temperature is higherthan the first temperature.

A plasma control program may include code for setting RF power levelsand exposure times in one or more process stations in accordance withthe embodiments herein. In some embodiments, the controller includesinstructions for depositing a protective layer at a first RF power leveland RF duration, and depositing an electrically favorable layer over theprotective layer at a second RF power level and RF duration. The secondRF power level and/or the second RF duration may be higher/longer thanthe first RF power level/duration.

In some embodiments, there may be a user interface associated withsystem controller 2450. The user interface may include a display screen,graphical software displays of the apparatus and/or process conditions,and user input devices such as pointing devices, keyboards, touchscreens, microphones, etc.

In some embodiments, parameters adjusted by system controller 2450 mayrelate to process conditions. Non-limiting examples include process gascomposition and flow rates, temperature, pressure, plasma conditions(such as RF bias power levels and exposure times), etc. These parametersmay be provided to the user in the form of a recipe, which may beentered utilizing the user interface.

Signals for monitoring the process may be provided by analog and/ordigital input connections of system controller 2450 from various processtool sensors. The signals for controlling the process may be output onthe analog and digital output connections of process tool 2400.Non-limiting examples of process tool sensors that may be monitoredinclude mass flow controllers, pressure sensors (such as manometers),thermocouples, etc. Appropriately programmed feedback and controlalgorithms may be used with data from these sensors to maintain processconditions.

System controller 2450 may provide program instructions for implementingthe above-described deposition processes. The program instructions maycontrol a variety of process parameters, such as DC power level, RF biaspower level, pressure, temperature, etc. The instructions may controlthe parameters to operate in-situ deposition of film stacks according tovarious embodiments described herein.

The system controller will typically include one or more memory devicesand one or more processors configured to execute the instructions sothat the apparatus will perform a method in accordance with the presentinvention. Machine-readable, non-transitory media containinginstructions for controlling process operations in accordance with thepresent invention may be coupled to the system controller.

1. A method of forming a silicon-containing bilayer on an exposedsurface of a reaction-sensitive substrate, comprising: (a) forming afirst layer of a silicon-containing film by a first plasma-enhancedatomic layer deposition process; and (b) forming a second layer of thesilicon-containing film by a second plasma-enhanced atomic layerdeposition process, wherein operation (b) is performed at a highertemperature than operation (a).
 2. The method of claim 1, wherein thefirst layer of silicon-containing film is between about 1 and 20% of atotal thickness of the bilayer.
 3. The method of claim 1, wherein athickness of the first layer of silicon-containing film is between about10 and about 50 Angstroms.
 4. The method of claim 1, wherein the firstplasma-enhanced atomic layer deposition process uses an oxidizingreactant comprising between about 50 and 100% weak oxidizer selectedfrom the group consisting of CO, CO₂, NO, NO₂, N₂O, sulfoxides,oxygen-containing hydrocarbons (C_(x)H_(y)O_(z)), and/or H₂O, andbetween about 0 and 50% O₂.
 5. The method of claim 1, wherein theexposed surface of the reaction-sensitive substrate is selected from thegroup consisting of silicon (Si), cobalt (Co),germanium-antimony-tellurium (GST), silicon-germanium (SiGe), siliconnitride (SiN), and silicon carbide (SiC).
 6. The method of claim 1,wherein the silicon-containing film is a silicon oxide, a siliconnitride, a silicon carbide, a silicon oxynitride, a silicon oxycarbide,or a silicon nitrogen carbide film.
 7. The method of claim 1, wherein athickness of the first layer of silicon-containing film is determinedby: (i) providing a plurality of individual substrates having differingthicknesses of silicon-containing protective films deposited thereon;(ii) measuring a pre-plasma thickness of each of the protective films onthe individual substrates; (iii) after (ii), exposing the individualsubstrates to a plurality of plasma exposure cycles, whereinsubstantially no material is deposited during the plasma exposure; (iv)after (iii), measuring a post-plasma thickness of the protective filmson the individual substrates; (v) calculating a thickness difference foreach individual substrate, the thickness difference corresponding to thepre-plasma thickness minus the post-plasma thickness; (vi) determiningthe thickness of the first silicon-containing film by evaluating theprotective film thickness at which the thickness difference becomessubstantially stable.
 8. A method of forming a silicon-containingbilayer on a reaction-sensitive substrate, comprising: (a) forming afirst layer of a silicon-containing film by a plasma-enhanced atomiclayer deposition process; and (b) forming a second layer of thesilicon-containing film on the first layer by a plasma-enhanced atomiclayer deposition process, wherein operation (b) is performed using ahigher radio frequency power than in operation (a).
 9. The method ofclaim 8, wherein the first layer of silicon-containing film is betweenabout 1 and 20% of a total thickness of the bilayer.
 10. The method ofclaim 8, wherein a thickness of the first layer of silicon-containingfilm is between about 10 and about 50 Angstroms.
 11. The method of claim8, wherein the first plasma-enhanced atomic layer deposition processuses an oxidizing reactant comprising between about 50 and 100% weakoxidizer selected from the group consisting of CO, CO₂, NO, NO₂, N₂O,sulfoxides, oxygen-containing hydrocarbons (C_(x)H_(y)O_(z)), and/orH₂O, and between about 0 and 50% O₂.
 12. The method of claim 8, whereinthe exposed surface of the reaction-sensitive substrate is selected fromthe group consisting of silicon (Si), cobalt (Co),germanium-antimony-tellurium (GST), silicon-germanium (SiGe), siliconnitride (SiN), and silicon carbide (SiC).
 13. The method of claim 8,wherein the silicon-containing film is a silicon oxide, a siliconnitride, a silicon carbide, a silicon oxynitride, a silicon oxycarbide,or a silicon nitrogen carbide film.
 14. The method of claim 8, wherein athickness of the first layer of silicon-containing film is determinedby: (i) providing a plurality of individual substrates having differingthicknesses of silicon-containing protective films deposited thereon;(ii) measuring a pre-plasma thickness of each of the protective films onthe individual substrates; (iii) after (ii), exposing the individualsubstrates to a plurality of plasma exposure cycles, whereinsubstantially no material is deposited during the plasma exposure; (iv)after (iii), measuring a post-plasma thickness of the protective filmson the individual substrates; (v) calculating a thickness difference foreach individual substrate, the thickness difference corresponding to thepre-plasma thickness minus the post-plasma thickness; (vi) determiningthe thickness of the first silicon-containing film by evaluating theprotective film thickness at which the thickness difference becomessubstantially stable.
 15. The method of claim 8, wherein forming thefirst layer of the silicon-containing film by the first plasma-enhancedatomic layer deposition process in (a) comprises: (i) periodicallyexposing the reaction-sensitive substrate to a vapor phase flow of asilicon-containing reactant in a station of a reaction chamber; (ii)exposing the reaction-sensitive substrate to a vapor phase flow of anoxidizing reactant or nitrogen-containing reactant in the station of thereaction chamber; and (iii) periodically igniting a plasma in thereaction chamber using a high frequency radio frequency power betweenabout 12.5 and about 125 Watts per station when the vapor phase flow ofthe silicon-containing reactant has ceased to thereby form the firstlayer of the silicon-containing film, wherein the plasma forms betweentwo electrodes, and wherein the reaction-sensitive substrate ispositioned between the two electrodes.
 16. The method of claim 15,wherein forming the second layer of the silicon-containing film by thesecond plasma-enhanced atomic layer deposition process in (b) comprises:(i) periodically exposing the reaction-sensitive substrate to a secondvapor phase flow of a second silicon-containing reactant in the stationof the reaction chamber; (ii) exposing the reaction-sensitive substrateto a second vapor phase flow of a second oxidizing reactant or a secondvapor phase flow of a second nitrogen-containing reactant in the stationof the reaction chamber; and (iii) periodically igniting the plasma inthe reaction chamber using a high frequency radio frequency powerbetween about 250 and about 1500 Watts per station when the vapor phaseflow of the second silicon-containing reactant has ceased.
 17. Themethod of claim 1, wherein forming the first layer of thesilicon-containing film by the first plasma-enhanced atomic layerdeposition process in (a) comprises: (i) periodically exposing thereaction-sensitive substrate to a vapor phase flow of asilicon-containing reactant in a station of a reaction chamber; (ii)exposing the reaction-sensitive substrate to a vapor phase flow of anoxidizing reactant or nitrogen-containing reactant in the station of thereaction chamber; and (iii) periodically igniting a plasma in thereaction chamber when the vapor phase flow of the silicon-containingreactant has ceased to thereby form the first layer of thesilicon-containing film, wherein the plasma forms between twoelectrodes, wherein the reaction-sensitive substrate is positionedbetween the two electrodes, and wherein a substrate temperature ismaintained between about 5° C. and about 200° C. during (a).
 18. Themethod of claim 17, wherein forming the second layer of thesilicon-containing film by the second plasma-enhanced atomic layerdeposition process in (b) comprises: (i) periodically exposing thereaction-sensitive substrate to a second vapor phase flow of a secondsilicon-containing reactant in the station of the reaction chamber; (ii)exposing the reaction-sensitive substrate to a second vapor phase flowof a second oxidizing reactant or a second vapor phase flow of a secondnitrogen-containing reactant in the station of the reaction chamber; and(iii) periodically igniting the plasma in the reaction chamber when thevapor phase flow of the second silicon-containing reactant has ceased,wherein the plasma forms between two electrodes, and wherein thereaction-sensitive substrate is positioned between the two electrodes,and wherein a substrate temperature is maintained between about 300° C.and about 400° C. during (b).